Tractor-trailer fluid pressure brake monitoring system

ABSTRACT

The invention provides a trailer brake monitoring system in which foot brake applications for normal braking and hand control braking for selectively applying the trailer brakes are separately monitored by respective monitoring switch circuits. Signals from the monitoring circuits are processed so as to provide a record of the duration and the count of such applications thus providing a record of the manner of brake usage. A solenoid-operated security system which can be locked and unlocked by a key is interconnected with the fluid supply to the trailer brakes.

FIELD OF THE INVENTION

The invention relates to a tractor-trailer fluid pressure brake systemof the type in which a first brake valve, usually operated by thedriver's foot brake pedal, is operable to release fluid for applying thebrakes of the tractor and of the trailer simultaneously, and a secondbrake valve, usually operated by a driver's hand control, is operableindependently of the first brake valve to release fluid for applying thetrailer brakes selectively. Nowadays, systems of this type are generallyair brake systems. The invention also provides a security system forlocking the trailer brakes when the trailer is parked so as to preventtheft.

BACKGROUND OF THE INVENTION

In such a braking system, normal braking is effected by means of thefoot brake pedal, i.e. by operation of the first brake valve, the handcontrol being operated only in special situations or in an emergency.However, in practice, misuse of the hand control occurs. Such misuseoccurs primarily in the case of freight companies which engageindependent owner-operators to pull their trailers, the owner-operatorsconserving their own tractor brakes by making excessive use of the handcontrol rather than by applying normal braking using the foot brakepedal. This practice results in excessive wear on the trailer brakes,broken brake drums, and increased tire wear. Moreover, the practice isan impediment to the safe operation of the unit since the condition oftrailer brakes which have been used improperly and excessively cannot begauged by the standard procedure based on mileage.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide means formonitoring the usage of the tractor and/or trailer brakes, moreparticularly the selective usage of the trailer brakes, whereby toprovide additional information relevant to the actual brake wear andinformation for the control of misuse of selective braking.

Accordingly, the invention provides, in a tractor-trailer fluid pressurebrake system of the type referred to above, an improved tractor-trailerbrake monitoring system comprising circuit means including a monitoringswitch responsive to operation of the second brake valve for producing asignal in accordance with the operation thereof, and a timer circuitinterconnected with the circuit means and responsive to said signal forregistering the duration of selective trailer brake usage. Preferablythe system also includes a counter circuit responsive to said signal forregistering the count of selective trailer brake applications. Byproviding a second monitoring switch response to hard brakingapplications, and a separate timer and/or counter circuit responsive tothe second monitoring switch, additional information relevant to trailerbrake wear can readily be derived.

In an alternative, simpler form of the invention, there is provided forthe tractor of a tractor-trailer combination a brake monitoring systemcomprising circuit means including a monitoring switch responsive tooperation of the hand control for producing a signal in accordancetherewith, and means responsive to said signal for registering selectiveoperation of the trailer brakes.

The emergency/parking brakes of the trailer are usually fluid-operatedspring brakes which, in normal road operating conditions are releasedfrom a locked condition by fluid supplied from the tractor, the brakesautomatically being biased to the locked condition in the event of lossof fluid pressure. For such a system the invention provides securitymeans to prevent unauthorized release of the brakes when the trailer isparked. The security means comprises a momentary contact double-solenoidvalve for controlling the supply of fluid to the brakes, circuit meansinterconnected with the solenoids of the valve for energizing thesolenoids, and the circuit means including a key-operated double-throwswitch having a normally open contact and a normally closed contact, thenormally open contact being in series with the valve solenoid operableto close the valve, and the normally closed contact being in series withthe valve solenoid operable to open the valve and with a manuallyoperable resetting switch.

In a preferred embodiment of the invention, the monitoring systemprovides means for registering system operational time in response tothe operation of a "power-on" switch, such as an oil pressure switchresponsive to engine oil pressure, and means for registering theduration and count of normal brake applications in response to theoperation of a stop light switch.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, one embodimentthereof will now be described, by way of example, with reference to theaccompanying drawings. In the drawings:

FIG. 1 is a schematic side elevation of a tractor-trailer unit, thetractor and trailer being shown separated to reveal the fluid supplyconnections;

FIG. 1a is a view of the standard electrical plug which is normallyinstalled on the back of the tractor;

FIG. 1b is a view of the standard receptacle which is normally installedon the trailer to receive the plug;

FIG. 2 is a diagram of the standard trailer connections provided by thereceptacle of FIG. 1b;

FIG. 3 is a diagram of a typical tractor-trailer air brake systemshowing the positions of certain switches used to derive signals for themonitoring system;

FIG. 4 is a schematic block diagram of the monitoring system;

FIG. 4a is a detailed wiring diagram of the blocks shown in FIG. 4;

FIG. 5 shows a detail of the monitoring system;

FIG. 6 shows a modification of the detail shown in FIG. 5;

FIG. 7 illustrates the electrical circuitry of a security system for thetrailer; and

FIG. 8 shows further details of the trailer security system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 shows a typical tractor-trailercombination incorporating an air brake system and a trailer brakemonitoring system in accordance with the present invention. Inaccordance with conventional practice the tractor 10 supplies brakingfor the simultaneous operation of the tractor brakes and trailer brakesby means of an engine-driven compressor, the desired air pressure beingregulated and maintained. Braking air for the brakes of the trailer 11is supplied via air lines 12, 13. The air line 12 is a service line usedfor normal braking, while the air line 13 is the supply line used onlyfor parking and emergency braking. The trailer emergency/parking brakesare fluid-operated spring brakes which are biased towards a lockingposition, but which are normally released from the locking position byair supplied from the tractor over the line 13. In the event of loss ofair pressure, the trailer brakes automatically close to the lockedcondition. Electrical connections between the tractor 10 and the trailer11 are provided by a standard 7-pin electrical plug 14 (FIG. 1a) mountedat the back of the tractor 10, and a standard receptacle 15 (FIG. 1b )mounted on the trailer 11 and adapted to receive the plug 14. FIG. 2shows the most usual arrangement of pin connections, which have tosupply current for the trailer tail lights, marker lights, turnindicator lights and stop lights.

FIG. 3 shows the general layout of a conventional tractor-trailer airbrake system which has been modified to incorporate a monitoring switch16 for monitoring hand brake operations. In this system air is suppliedby an engine-driven compressor 17 to a supply reservoir 18 and to aservice reservoir 19 via a check valve 20. The compressor 17 isregulated by a governor 21 which, together with a safety valve 22 on thesupply reservoir, maintains the air pressure at 120 p.s.i. From theservice reservoir 19 air is supplied to the tractor brakes 23 via asupply line 24, a foot brake valve 25, an air line 26, and a quickrelease valve 27 in accordance with the operation of the foot brakevalve 25. Similarly, air is supplied to the tractor brakes 28 via thesupply line 24, foot brake valve 25, an air line 29 and a quick releasevalve 30. At the same time, in accordance with the operation of the footbrake valve, air is delivered to the trailer service brakes 31a via thesupply line 24, air line 32, valve 33 and trailer reservoir 70. Thus,since normal braking is effected by means of the foot brake valve 25,the tractor brakes and the trailer brakes are applied simultaneouslyunder one control. It is to be noted that the foot brake valve 25 iscoupled via a double check valve 34 to a stop light switch 35, which inthe present example is an air switch responsive to braking air pressure.

For use in special situations or in an emergency, the system is providedwith a second brake valve 36 operated by a driver's hand control 37. Thebrake valve 36 interconnects the supply line 24 with a delivery line 38.This is connected via the double check valve 34 to the air line 32 foractivating the trailer brakes 31. When the hand control valve 36 isoperated, the foot brake valve 25 remaining closed, the double checkvalve 34 is positioned to divert the braking air only along the line 32so that the trailer brakes are activated selectively, that is to say,without application of the tractor brakes 23, 28.

In the present invention, the monitoring switch 16 is provided formonitoring the operation of the hand control valve 36. It could be anyswitching element electrically or mechanically coupled to the handcontrol, but in the present example it is shown as an air switchresponsive to air pressure in the air delivery line 38.

As will be described hereinafter, the trailer emergency/parking brakes31b are pneumatically operated spring brakes biased towards a lockingposition, but normally released from the locking position by pressurizedair supplied from the tractor via a momentary contact double solenoidvalve 39 and a supply line 40.

Referring now to FIGS. 4 and 5, the monitoring switch 16 is normallyclosed and is connected in series with a normally open "power-on" switch41, the latter being responsive to engine oil pressure when the tractorengine is turned on. The switches 16 and 41 are connected in circuitbetween the tractor battery positive terminal and the auxiliary pin (pinNo. 7) of the plug connector 14. The stop light switch 35 is connecteddirectly to pin No. 4 of the plug connector 14, and the supply for thetrailer marker lights is connected via pin No. 2. Pin No. 1 is grounded.

As shown in FIG. 4, the trailer carries a registration system forregistering the duration and count of different brake applicationsduring the operational time of the tractor. For the system shown, asecond monitoring switch 42 is mounted on the trailer. This is an airswitch coupled to the air service line 12 in such a way as to respond tobraking air pressure over a predetermined level, thereby to provide a"hard braking" signal. Also shown is a security circuit, generallydesignated by the reference 43, which will be described subsequently.

The registration system comprises an interface 44 which is a gatingdevice for processing signals from the monitoring switch circuits, sixcontrol modules 45, 46, 47, 48, 49 and 50, five timer circuits 51, 5253, 54 and 55, and four counter circuits 56, 57, 58 and 59. In thepresent example the interface 44, as well as each of the control modules45-50, is an ITT Module Type LZ 12SPDT. FIG. 4a is a schematic showingthe interconnections of these modules. The counters are Hecon countersType 0.664.7. Each of the timers is a Hecon timer with short timestorage feature.

In normal operation of the system, the oil switch 41 is closed inresponse to "power-on", causing a signal to be applied via the normallyclosed switch 16 to the auxiliary pin No. 7 of the connector 15. Thesignal is applied to the timer 51 via the interface 44 and the controlmodule 45, thereby operating the timer for the duration of the appliedsignal and so registering the system operational time. No other signalsare applied to the registration system in the absence of trailerbraking. In the event of normal braking by application of the foot brakevalve 25, a signal is applied from the circuit containing stop lightswitch 35 via terminal pin No. 4 to the interface 44. The processedsignal is applied to the timer 52 and the counter 56 via the controlmodule 46. In this case, the timer 52 registers and accumulates theduration of braking applications and the counter 56 registers the numberof times that braking is applied.

In the event of braking via the hand control 37, the monitoring switch16 is opened, the signal flow being interrupted to the interface 44. Atthe same time a signal from the stop light switch circuit is applied tothe interface 44 via pin No. 4. In this case the output of the interface44 is applied via the control module 47 to the timer 53 and the counter57, the former registering and accumulating the duration of hand controlbraking applications and the latter registering the count of suchapplications.

The second monitoring switch 42, as previously mentioned, is conditionedto respond to air line pressure above a predetermined level and so torespond to hard braking applications. Signals from the hard brakingmonitoring switch 42 are applied to control modules 48 and 49, whichalso are connected so as to differentiate foot brake applications fromhand control brake applications. The resultant signals are applied to atimer 54 for reqistering and accumulating the duration of hard brakingapplications by the hand control valve, to the timer 55 for registeringand accumulating the duration of all foot brake pedal hard brakingapplications, to the counter 58 for registering the count of hardbraking applications by the hand control valve, and to the counter 59for registering the count of all foot brake pedal hard brakingapplications.

In the system described above, the connections to the pins of theelectrical connector are appropriate so long as the auxiliary terminalNo. 7 is not required for other purposes. In certain cases it is usedfor other purposes, as when the trailer is equipped with a third axle orother electrical auxiliary equipment. In this case, the monitoringsystem can suitably be powered through the trailer marker light terminalNo. 2, shown in FIG. 6. This is achieved by disconnecting the markerlight switch located on the tractor dashboard and use of the power fromthe marker light relay 61. Thus, in this case, power is supplied throughthe oil switch 41 through the closed monitoring switch 16 and thetrailer marker light relay 61, which will supply continuous power to pinNo. 2 of the plug connector.

With this modification, the trailer marker lights will remain on whilethe unit is in use, except for short time periods when the trailer handbrake control is activated.

The monitoring system can also be suitably powered if terminal No. 7 isrequired for other purposes by joining the marker light wire to the taillight wire on the tractor and trailer. Thus, using only one terminal,No. 6, to power the marker and tail lights. In this case the terminalNo. 2 becomes free to power the monitoring system instead of terminalNo. 7.

The security system generally designated 43 in FIG. 4 is shown moreclearly in FIG. 7 and FIG. 8. FIG. 7 more particularly shows theelectrical circuitry of the security system while FIG. 8 shows thepositioning of the double solenoid valve with respect to the air supply.As previously mentioned, the trailer emergency/parking brakes are springbrakes which are adapted to be released and held from the lockedposition by air supplied from the tractor over an air line 13. (FIG. 1).Loss of line air pressure, whether caused by a fault in the air systemor caused intentionally for parking purposes, will result in automaticlocking of the brakes. This is a well known system. In the presentinvention, however, means are provided for preventing unauthorizedrelease of the trailer brakes whereby to prevent theft of the trailerwhen it is unattended. This is achieved by means of a double solenoidvalve 39 arranged in the air line 40 (see also FIG. 3), the solenoidvalve being operable to control the supply of air to the traileremergency/parking brakes. A suitable solenoid valve is the Type 6159CJM-5/2-1/4-FH supplied by Festo Inc. The valve 39 has a closure memberwhich, in one condition of the valve shuts off the flow of braking airinto passage 40, thereby causing the brakes to lock, and in anothercondition of the valve permits flow of air for releasing the brakes. Thesolenoid valve 39 has a first solenoid 62 for setting the valve to theclosed condition when energized and a second solenoid 63 for resettingthe valve to the open condition. The solenoids are connected in circuitwith terminal pin No. 4 and No. 6 respectively of the trailer receptacleconnector 15, via a key-operated, double-throw switch 64. The switch 64has a normally open contact 65 connected in circuit between terminal pinNo. 4 and the solenoid 62, the return to ground being by way of terminalpin No. 1. The switch 64 also has a normally closed contact 66 connectedin circuit with a normally open, manually operable, push-button switch67 between the terminal pin No. 6 and the solenoid 63, the return toground being by way of terminal pin No. 1. A display device 68, operableby the double-throw switch 64 in the "valve closed" condition, isprovided for displaying the status of the security system.

Under normal operating conditions the double solenoid valve 39 is, ofcourse, open. In order to secure the trailer when it is being parked,the trailer marker lights must first be "ON". The operator must thenswitch over the key-operated double-throw switch 64 by turning the keyin the switch lock, thereby closing contact 65 and opening contact 66.This will close the circuit of the solenoid 62 and so close the valve39, provided that the operator re-enters the tractor and releases andreactivate the trailer parking brakes. The trailer brakes will now belocked and will remain locked. In order to release the brakes it isnecessary first to couple the trailer to a tractor, switch the markerlights on, deactivate the security system by switching the double-throwswitch over to its first position and finally to reset the system bypressing the push button switch 67, reopening the valve 39.

What I claim is:
 1. In a tractor-trailer fluid pressure brake system inwhich a driver-operated first brake valve is operable to release fluidfor applying the tractor and trailer brakes simultaneously, and adriver-operated second brake valve is operable independently of thefirst brake valve to release fluid for applying the trailer brakesselectively, an improved tractor-trailer brake monitoring systemcomprisingcircuit means including a monitoring switch responsive tooperation of the second brake valve for producing a signal in accordancewith operation thereof, and a timer circuit interconnected with saidcircuit means and responsive to said signal for registering the durationof selective trailer brake usage.
 2. A tractor-trailer brake monitoringsystem according to claim 1, further comprising a counter circuitresponsive to said signal for registering the count of selective trailerbrake applications.
 3. In a tractor-trailer fluid pressure brake systemin which a driver-operated first brake valve is operable to releasefluid for applying the tractor and trailer brakes simultaneously, and adriver-operated second brake valve is operable independently of thefirst brake valve to release fluid for applying the trailer brakesselectively, an improved tractor-trailer brake monitoring systemcomprisingcircuit means including a monitoring switch responsive tooperation of the second brake valve for producing a signal in accordancewith operation thereof, and a counter circuit interconnected with saidcircuit means and responsive to said signal for registering the count ofselective trailer brake applications.
 4. In a tractor-trailer fluidpressure brake system in which a driver-operated first brake valve isoperable to release fluid under pressure for applying the tractor brakesand trailer brakes simultaneously, and a driver-operated second brakevalve is operable independently of the first brake valve to releasefluid under pressure for applying the trailer brakes selectively, thesystem further comprising first circuit means including a power-onswitch responsive to tractor operation, and second circuit meansincluding a stop-light switch responsive to brake applications, animproved tractor-trailer brake monitoring system comprisinga first timercircuit interconnected with said first circuit means for registeringsystem operational time, a second timer circuit interconnected with saidsecond circuit means for registering trailer brake usage time, thirdcircuit means including a monitoring switch responsive to operation ofthe second brake valve for producing a signal in accordance withoperation thereof, and a third timer circuit interconnected with saidthird circuit means and responsive to said signal for registering theduration of selective trailer brake usage.
 5. A tractor-trailer brakemonitoring system according to claim 4, further comprisinga firstcounter curcuit interconnected with said second circuit means andresponsive to stop-light switch operation for registering the count ofbrake applications, and a second counter circuit interconnected withsaid third circuit means and responsive to said monitoring switchoperation for registering the count of selective trailer brakeapplications.
 6. A tractor-trailer brake monitoring system according toclaim 4, further comprisingfourth circuit means including a secondmonitoring switch responsive to service line fluid pressure above apredetermined level, a fourth timer circuit interconnected with saidfourth circuit means and responsive to operation of the secondmonitoring switch for registering the duration of hard brakingapplications by the first brake valve, and a fifth timer circuitinterconnected with said fourth circuit means and said third circuitmeans for registering the duration of hard braking applicationsselectively applied to the trailer brakes as detected by the concurrentoperation of the first and second monitoring switches.
 7. Atractor-trailer brake monitoring system according to claim 6, furthercomprisinga third counter circuit interconnected with said fourthcircuit means and responsive to operation of the second monitoringswitch for registering the count of hard braking applications by thefirst brake valve, and a fourth counter circuit interconnected withfourth circuit means and said third circuit means for registering thecount of hard braking applications selectively applied to the trailerbrakes as detected by the concurrent operation of the first and secondmonitoring switches.